Integrated rock magnetic and mineralogical study of the Lower Triassic sedimentary rocks from Spitsbergen

Abstract

Abstract A rock magnetic, mineralogical and Mossbauer spectroscopy study was undertaken on the Lower Triassic sediments from the West Spitsbergen Fold and Thrust Belt (WSFTB) in Svalbard as well as the foreland of this orogen for a thorough recognition of magnetic mineralogy, necessary for a better-constrained interpretation of paleomagnetic results. SEM and Mossbauer spectroscopy indicate the presence of magnetite and pyrrhotite, both most probably of secondary origin but altered clasts of volcanic origin and grains of ilmenite and detrital magnetite are also observed. Thermomagnetic curves of whole-rock samples exhibit paramagnetic behavior whereas ferromagnetic separates indicate the presence of magnetite. IRM component analysis shows three major contributors – magnetite, hematite, and pyrrhotite to the remanence, with ferromagnetic iron oxides the most dominant. Identified ferromagnetic minerals display a wide range of grain-size and magnetic behavior, with the domination of PSD particles. Rock magnetic characteristics of both areas are similar, but sites in the fold belt were most likely remagnetized, whereas those in the foreland carry the primary magnetization. The age of remagnetization was estimated as pre-Eurekan related to rift-controlled Mesozoic extensional phases of the Barents Sea Shelf (Clark et al., 2014) and/or Cretaceous injections of dolerites in the Svalbard Archipelago (Nejbert et al., 2011) as well as early stages of the WSFTB formation. However, Triassic remanence might persist in volcanic lithoclasts and detrital magnetite indicated along the WSFTB. The multicomponent nature of the NRM, displaying a broad range of grain size, might impede the paleomagnetic interpretation of Triassic rocks in Spitsbergen.